Process of preparing an X-ray sensitive member



United States PatentO PROCESS OF PREPARING AN X-RAY SENSITIVE MENEER Osmar A. Ullrich, Jr., Worthington, Ohio, assignor, by

mesne assignments, to The Battelle Development Corporation, Columbus, Ohio, a corporation of Ohio No Drawing. Application August 19, 1952, Serial No. 305,280

3 Claims. (Cl. 117-49) This invention relates to electrophotographic radiography plates or xeroradiographic plates and to methods of preparing such plates. More particularly, the invention relates to xeroradiographic plates which are sensitive to X-ray radiations and substantially insensitive to visible light, whereupon they may be employed in radiography in the presence of general illumination.

In the past, it has been usual to employ, for radiography, films, plates, or the like, which are sensitive to visible light as well as to X-ray radiation so that it has been necessary to store and use the process these films or plates in darkness. It is desirable, of course, that techniques for radiography be made as simple and adaptable as possible, and thus the sensitivity to visible light of such members is frequently disadvantageous. Now, in accordance with the present invention, there is provided a radiographic member substantially exclusively sensitive to the X-ray, or like radiation, and characterized by being insensitive to visible light, whereby many advantages can be achieved.

It is, therefore, an object of this invention to provide a new and useful radiographic sensitive member.

Another object of the present invention is to provide a xerographic member which is sensitive and responsive to X-ray radiations, but which is insensitive to visible light.

Yet another object of this invention is to provide an X-ray sensitive xeroradiographic member insensitive to visible light which plate may be used repeatedly in providing X-ray or radiographic prints.

Other objects and advantages of the invention will be apparent from the following detailed description and disclosure thereof.

In general, the radiographic member of this invention comprises a conductive backing member and an X-ray sensitive coating layer comprising a selenium layer deposited upon the conductive backing member while such backing member is maintained at a temperature in the range from about 25 C. to about 35 C. In the preparation of the sensitive members of the present invention, it is important and critical that the temperature of the backing be maintained within the range of about 15 C. to 35 C. and it is preferred that the temperature be maintained in the range from 25 C. to 30 C. while selenium is being deposited thereon, preferably under vacuum in the order of about 1 micron of mercury, or less, with the result that the selenium is deposited in a form preferentially and apparently exclusively suited for radiographic exposures. The selenium deposit thus formed is substantially indistinguishable by visual examination from vitreous selenium formed under other conditions such as, for example, deposition at higher temperatures, and is differentially distinguishable therefrom by its electrical properties, particularly by the selectivity of its photosensitivity to X-ray and like radiation and insensitivity to visible light.

By way of illustration, and with no intent of limitation, the method of producing a member, such as a plate, of

Patented Aug. 27, 1957 this invention will be described in connection with a metal backing plate, for example, a brass plate. The backing member may be prepared for coating by any of various cleaning or pre-treatment steps or processes, such as, for example by polishing, or the like. The cleaned plate is then positioned in a vacuum container or chamber with temperature-control means for the backing member such as, for example, a contacting temperature-control platen, provided, for example, with water-cooling means. This container or chamber is evacuated to a low pressure, such as about 1 micron of mercury, or less, for example about 0.5 micron. A layer of selenium is then evaporated onto the plate, for example, from refractory containers such as molybdenum boats, or the like, the coating being preferably about 5 to about microns thick, desirably about 20 to about 50 microns. Throughout the coating and vaporizing process, it is important, essential, and highly critical that the temperature of the backing plate be maintained below 357 0, generally within the range 1535 C., and preferably within the range 2530 C. If the advantages of this invention are to be realized, the temperature of the backing plate in no case may be permitted to exceed 35 C. during the process of making the plate.

As a specific example of the manner in which the plate of the present invention may be formed, the following detailed description is ofifered:

Example A brass backing plate was thoroughly cleaned and polished with a wax base polish under the name Glass Wax. The polished plate was vapor degreased using isopropyl alcohol as the solvent, and then placed in position in a vacuum chamber. The pressure in the chamber was reduced to 0.2 micron and a 50 micron layer of selenium was evaporated onto the backing plate from molybdenum boats, which were heated by electric current passed therethrough. During the evaporation procedure, the temperature of the brass backing was maintained between 25 C. and 30 C. The coated plate was capable of accepting an electrostatic charge on its selenium surface of at least 400 volts positive polarity either in the absence of illumination, or when exposed to white visible light. When exposed to X-ray activating radiation, the resistivity of the selenium layer dropped by several orders of magnitude, whereby an electrostatic charge on the selenium layer was dissipated.

Plates, prepared in the manner described above, may be used in producing X-ray photographs in the following manner:

The plate first is sensitized by being subjected to a corona discharge, or other electrical charge-producing means, whereupon an electrical charge desirably, but not necessarily, of positive polarity is deposited upon the plate. This step may be carried out in an ordinarily lighted room, or even in a highly illuminated room normally lighted with visible light but substantially free from X-rays, or the like. This is contrary to the situation in regard to previous films and plates for use in X-ray processes, which require complete shielding from light until after the. exposure and development of the X-ray image.

An article to be X-rayed is placed between the charged plate and an X-ray source, or positioned in any other manner as desired relative to the plate and the X-ray source common to the X-ray art. The X-ray source is energized and the positively charged plate is exposed to the radiations through the object being tested or X-rayed. Those areas of the positively charged plate which are struck by the X-rays become electrically more conductive by several orders of magnitude under the action of the X-rays and the electrostatic charges on those areas leak otf through the plate, leaving a latent image formed of positive electric charges on those areas not struck by the penetrating rays. This latent image may readily be made visible by contacting it with any oneof a number of electroscopic materialssuch as clouds, mists, and.

the like, or the flow of finely divided electroscopicmaterial which will adhere preferentially to the charged areas and not tothe non-image, or uncharged, portions of the plate. According to one method of development, the developer may consist of two components, one a powder component and the other a granular carrier com ponent, as described and claimed in application Serial Number 762,005, now Patent 2,618,552. Othermethods of development may be used as desired.

If a print of the radiographic picture be desired, the developed powder image may be transferred from the plate to a second surface; for example, transfer may be made to an adhesively coated paper, or other adhesive material. Transfer may also be effected electrically by placing an image-receiving material (such as a sheet of paper) in contact with the powder image and subjecting the back, or exposed side of such material to an ion dis charge, such as discharge from corona Wires or needles. Once the powder image has been transferred, it may be permanently fixed to the transfer material. For example, resinous powders may be fused thereto by heat, solvent, or the like. I

Once the X-ray image has been transferred from the plate, or examined, or recorded by other methods or means, the plate may be prepared for re-use by cleaning off any remaining powder particles. 'This may be done by any of several methods, such as for example, the method of U. S. Patent.2,484,782. A new and independent X-ray image may then be formed on the plate by repeating the steps enumerated above. In addition to the brass backing member, as hereinbefore disclosed,

there may be and have been employed other metallic the entire process including the development process, a 5

distinct advantage, permitting, for example, the develop ment of the exact desired degree of contrast for each portion of the X-ray image, etc. The member is particularly adapted for field use and for operations where shielding from visible light is undesirable or inconvenient.

The new xeroradiographic member is differentially distinguished from prior members by the electrical properties and by its method of preparation, since the new member appears indistinguishable by visual examination, chemical test and even crystallographic analysis The selenium layer, according to this invention, has a specific resistivity in the order of about 10 to 10 ohm ,cms. or higher inrthe absence of illumination or in the presence of visible light. When exposed to penetrating radiation such as X-rays, this resistivity drops several orders of magnitude. Visually, the selenium layer is glassy in appearance and reddish black, being generally black upon visual examination in layers in the order of 20 to 50 microns thick. The layer appears essentially completely amorphous; it is believed and understood that the electrical properties may result from sub-crystalline structures or nucleation during the selenium deposition, although it is not intended to limit the invention to the theoretical probability of the existence of such sub-crystalline structures or nucleation.

Various departures and variations from the exact procedure described above, will be apparent to persons skilled in the art, and it is intended that these be included as a part of this invention, since they do not depart from the scope thereof. In view of the disclosure and description above, it is desired to protect by Letters Patent the present invention, as set forth in the attached claims.

What is claimed is:

1. The'process of preparing a xerographic member sensitive to X-rays and insensitive to visible light, comprising the step of yaporizing selenium onto an electrically conductive base member in a vacuum chamber maintained at a pressure of about 1 micron or less while maintaining such base plate at a temperature in the range 15 C. to 35 C.

2. The process of claim 1 wherein the selenium is vaporized onto the base member under vacuum in the range of less than about 1 micron of mercury.

3. The process according to claim '1 wherein the base plate temperature is maintained in the range from C. to C. throughout the vaporization.

. References Cited in the file of this patent V Schatfert et al. Jan. 12 

1. THE PROCESS FOR PREPARING A XEROGRAPHIC MEMBER SENSITIVE TO X-RAYS AND INSENSITIVE TO VISIBLE LIGHT, COMPRISING THE STEP OF VAPORIZING SELENIUM ONTO AN ELECTRICALLY CONDUCTIVE BASE MEMBER IN A VACUUM CHAMBER MAINTAINED AT A PRESSURE OF ABOUT 1MICRON OR LESS WHILE MAINTAINING SUCH BASE PLATE AT A TEMPERATURE IN THE RANGE 15*C. TO 35*C. 